As the need for high speed communication increases, new techniques and networks are required to improve the efficiency with which data can be transmitted. Several Digital Loop Carrier (“DLC”) systems have been introduced over the last few decades to address the need for high speed communication. A DLC is a telecommunications system that carries telephone signals from a Central Office to subscribers in a local loop using digital signals as a transport mechanism. The first DLC was introduced in the early 1970's to provide a cost-effective means for deployment of voice service in rural areas.
The local loop is necessary since Central Office equipment has an operational range limitation of 18,000 feet. This range is called the Central Office serving area. Subscribers living within that service area are the only subscribers who receive service directly from the Central Office. All other customers receive service from the DLC via Remote Terminals coupled to the local loop.
The Remote Terminals serve as service aggregation points for remote subscribers and are located along the local loop, which is often comprised of fiber optic cable. In operation, voice traffic bound for a subscriber is digitized and transported over the fiber optic cable to a Remote Terminal that services the target subscriber. Upon receipt of the digitized voice traffic, the Remote Terminal converts the digitized signal into an analog signal that is carried to the target subscriber's telephone via a twisted pair of copper wires. In this manner, telephone service is provided to remote subscribers.
In addition, T1 connections are used to deliver phone service to large entities such as corporations, hospitals, hotels, or universities having a large number of telephone lines that are interconnected yet require connection to the local loop.
This entire DLC implementation utilizes Time Division Multiplexing (“TDM”) elements. TDM refers to a technique in which data from multiple channels may be allocated bandwidth on a single medium (e.g., copper wire) based on a time slot assignment.
A more recent version of the DLC provides Asymmetrical Digital Subscriber Line (“ADSL”) service along with telephone service to a remote subscriber. This is made possible by transmitting signals for the telephone service and Digital Subscriber Line (“DSL”) service on the same line to a splitter within the Remote Terminal. The splitter is included to separate the frequencies for telephone service and DSL service. The voice traffic is sent back to the Central Office via the TDM infrastructure while the DSL service is sent back to the Central Office via a separate Asynchronous Transfer Mode (“ATM”) overlay network. In this system, the ATM traffic has limited access to the available bandwidth since at least a portion of the bandwidth has been previously dedicated to telephone service regardless of whether the dedicated bandwidth is actually being used at the time of ATM transmission.
In yet a later DLC, a Symmetrical High Bit Rate Digital Subscriber Line (“SHDSL”) is used to connect an Integrated Access Device (“IAD”) to a Digital Subscriber Line Access Multiplexer (“DSLAM”) located in the Remote Terminal. An IAD is customer premise equipment used for aggregating diverse traffic types such as voice and data. The IAD converts analog voice traffic to digital and sends the digitized voice traffic along with non-voice data. The ATM overlay in this system also shares bandwidth with the existing TDM infrastructure, which contains dedicated bandwidth that cannot be reallocated based on network traffic requirements.
All of the DLCs described above conform to the American National Standards Institute's ANSI T1.105-1995 et seq. and ANSI T1.119-1994 et seq. standards for a Synchronous Optical Network (“SONET”), which is a standard for synchronous data transmission on optical media. Typically, SONET is used in a fiber ring topology and supports electronic redundancy in the form of protection switching from a primary to a standby path when a network fault occurs. One problem with a SONET-based communication system is that SONET uses circuit switching with virtual circuits, which ties up bandwidth that cannot be reallocated based on network traffic requirements.